Method and apparatus for locating an acoustic source

• US 5,357,484 A
• Filed: 10/22/1993
• Issued: 10/18/1994
• Est. Priority Date: 10/22/1993
• Status: Expired due to Fees

• Current Assignee: the united states of america as represented by the secretary of the navy
• Original Assignee: the united states of america as represented by the secretary of the navy
• Inventors: Bates, Susan M., Bates, Bruce J.
• Primary Examiner(s): Lobo, Ian J.
• Application Number:
  US08/147,237
• Time in Patent Office: 361 Days
• Field of Search: 367/118, 367/124, 367/129, 367/131, 364/421
• US Class Current: 367/118
• CPC Class Codes: G01S 11/14 using ultrasonic, sonic, or infrasonic waves
• CPC Class Codes: G01S 3/8036 derived directly from separate directional systems

Abstract

An apparatus and method for determining the range and depth to an acousticource from a sampling site in a medium. A linear array of pressure transducers monitors the acoustic field produced by the acoustic source. A measurement processor utilizes the measured acoustic field to produce an initial field condition for each member of the array. An environmental model includes environmental data in the form of acoustically pertinent variables that define acoustic energy transfer characteristics through the medium at different ranges and depths. A backpropagation processor utilizes the initial field condition and the acoustically pertinent variables to produce, for each incremental range and depth, an amplitude function. An index processor normalizes the amplitude functions for each incremental range and depth, and an index extreme value processor selects the amplitude function with the maximum amplitude. The range and depth of that extreme value amplitude function is used to determine the range and depth for the acoustic source.

Claims

1. A method for determining the range and depth of an object in a given volume of a medium from a remote sampling site in the medium wherein the given volume is characterized by having a maximum range from the sampling site and wherein an acoustic field propagates from the object to the sampling site and the medium has known acoustically pertinent variables corresponding to known physical acoustic energy transfer characteristics at different ranges and depths throughout the medium, said method comprising the steps of:

sampling the distribution of the acoustic field at the sampling site as a function of depth;

processing the sampled acoustic field distribution and acoustically pertinent variables for each range and depth in an iterative process whereby during each iteration said processing generates a signal with a given amplitude; and

locating a range and a depth at which the signal has an extreme value whereby the range and depth at which the extreme value exists are used to determine the range to and depth of the object.

2. A method as recited in claim 1 wherein said processing includes:

generating a field distribution during each iteration for an incremental range and depth based upon a backpropagation of an initial acoustic field.

3. A method as recited in claim 2 wherein said sampling includes:

obtaining simultaneously complex pressure readings from each of a plurality of predetermined depths at the sampling site; and

determining from the readings the initial acoustic field as a function of depth.

4. A method as recited in claim 3 wherein said locating of the range and depth includes:

generating an index signal having an amplitude corresponding to the amplitude of the backpropagation field at each incremental range and depth; and

determining the extreme value of the index signal based upon a maximum value thereof.

5. A method as recited in claim 2 wherein said processing includes generating an acoustic field distribution based upon the acoustic field at the sampling site by using an implicit finite difference solution to a wide angle parabolic equation according to

6. A method as recited in claim 2 wherein said processing includes generating an acoustic field distribution based upon the acoustic field at the sampling site by using an implicit finite difference solution to a wide angle parabolic equation.

7. A method as recited in claim 6 wherein said locating of the range and depth includes:

generating an index signal having an amplitude corresponding to the amplitude of the backpropagated field at the range and depth; and

determining the extreme value of the index signal based upon a maximum value thereof.

8. A method as recited in claim 7 wherein said sampling includes the steps of:

obtaining simultaneously complex pressure readings from each of a plurality of pressure transducers located in a vertical array at predetermined different depths; and

converting the readings for obtaining initial values at each of the transducers for providing an initial acoustic field distribution at the sampling site as a function of depth for use in said processing step.

9. A method as recited in claim 8 wherein the readings obtained from each pressure transducer have the form p(r,z;

ω

,t) and said conversion includes coherently processing the readings to obtain an initial value "P_c " given by

space="preserve" listing-type="equation">p.sub.c =<

p(r,z;

ω

,t)>

where "r" is the range, "z" is the depth, "ω

" is the frequency of the acoustic signal, "t" is the time, and "<

>

" represents an averaging of the function.

10. A method as recited in claim 8 wherein the readings obtained from each pressure transducer have the form p(r,z;

ω

,t) and said conversion includes incoherently processing the readings to obtain an initial value "P_r " given by

space="preserve" listing-type="equation">p.sub.I =p.sub.r =<

p*(r,z;

ω

,t)p(r,z;

ω

,t)>

.sup.1/2

where "r" is the range, "z" is the depth, "ω

" is the frequency of the acoustic signal, "t" is the time, "p*" represents the complex conjugate of the pressure function, and "<

>

" represents an averaging of the function.

11. A method as recited in claim 8 wherein said sampling includes obtaining simultaneously complex pressure readings from each of a plurality of predetermined depths at the sampling site by a corresponding plurality of pressure transducers and determining from the readings the initial acoustic field as a function of depth.

12. A method as recited in claim 11 wherein the readings obtained from each pressure transducer have the form p (r,z;

ω

, t) and said conversion includes coherently processing the readings to obtain an initial value "P_c " given by

space="preserve" listing-type="equation">p.sub.c =<

p(r,z;

ω

,t)>

where "r" is the range, "z" is the depth, "ω

" is the frequency of the acoustic signal, "t" is the time, and "<

>

" represents an averaging of the function.

13. A method as recited in claim 11 wherein the readings obtained from each pressure transducer have the form p(r,z;

ω

,t) and said conversion includes incoherently processing the readings to obtain an initial value "P_r " given by

space="preserve" listing-type="equation">p.sub.I =p.sub.r =<

p*(r,z;

ω

,t)p(r,z;

ω

,t)>

.sup.1/2

where "r" is the range, "z" is the depth, "ω

" is the frequency of the acoustic signal, "t" is the time, "p*" represents the complex conjugate of the pressure function, and "<

>

" represents an averaging of the function.

14. A method as recited in claim 1 wherein said locating of the range and depth includes:

generating an index signal having an amplitude corresponding to the amplitude of the backpropagated field at the range and depth;

determining the extreme value of the index signal based upon a maximum value thereof; and

determining the range to and depth of the object relative to the array.

15. A method as recited in claim 14 wherein said index signal generating step produces, for each iteration of said processing step, an index signal according to

16. Apparatus for determining the range and depth of an object in a given volume of a medium from a remote sampling site in the medium wherein the given volume is characterized by having a maximum range from the sampling site and wherein an acoustic field propagates from the object to the sampling site and the medium has known acoustically pertinent variables corresponding to known acoustic energy transfer characteristics at different ranges and depths throughout the volume, said apparatus comprising:

means for sampling the distribution of the acoustic field at the sampling site as a function of depth;

means for processing the sampled acoustic field distribution and the acoustically pertinent variables for each range and depth in an iterative process whereby during each iteration said processing means generates a signal with a given amplitude; and

means for locating a range and depth at which the signal has an extreme value whereby the range and depth at which the extreme exists is used to determine the range to and depth of the object.

17. Apparatus as recited in claim 16 wherein said processing means generates a field distribution during each iteration for an incremental range and depth based upon a backpropagation of an initial acoustic field.

18. Apparatus as recited in claim 17 wherein said sampling includes:

means for obtaining simultaneously complex pressure readings from each of a plurality of predetermined depths at the sampling site; and

means for determining from the readings the initial acoustic field as a function of depth.

19. Apparatus as recited in claim 18 wherein said locating of the range and depth includes:

index processor means for generating an index signal having an amplitude corresponding to the amplitude of the backpropagated field at each incremental range and depth; and

index extreme value processor means for determining the extreme value of the index signal based upon a maximum value thereof.

20. Apparatus as recited in claim 17 wherein said processing includes backpropagation processor means for generating an acoustic field distribution at successive incremental ranges and depths based upon the acoustic field at the sampling site by using an implicit finite difference solution to a wide angle parabolic equation according to

21. Apparatus as recited in claim 17 wherein said processing means includes backpropagation processor means for generating an acoustic field distribution at successive incremental ranges and depths based upon the acoustic field at the sampling site by using the backpropagation of an implicit finite difference solution to a wide angle parabolic equation.

22. Apparatus as recited in claim 21 wherein said locating means includes:

index processor means generating an index signal having an amplitude corresponding to the amplitude of the backpropagated field at each incremental range and depth; and

index extreme value processor means for determining the extreme value of the index signal based upon a maximum value thereof.

23. Apparatus as recited in claim 21 wherein said sampling means includes:

transducer array means for obtaining simultaneously complex pressure readings from each of a plurality of pressure transducers located in a vertical array at different predetermined depths; and

measurement processor means for converting the readings into initial values at each of the transducers thereby to obtain an initial acoustic field distribution at the sampling site as a function of depth for use by said processing means.

24. Apparatus as recited in claim 23 wherein the readings obtained from each pressure transducer means have the form p(r,z;

ω

,t) and said conversion means includes means for coherently processing the readings to obtain an initial value "P_c " given by

space="preserve" listing-type="equation">p.sub.c =<

p(r,z;

ω

,t)>

where "r" is the range, "z" is the depth, "ω

" is the frequency of the acoustic signal, "t" is the time, and "<

>

" represents an averaging of the function.

25. Apparatus as recited in claim 23 wherein the readings obtained from each pressure transducer means have the form p(r,z;

ω

,t) and said conversion includes means for incoherently processing the readings to obtain an initial value "P_r " given by

space="preserve" listing-type="equation">p.sub.I =p.sub.r =<

p*(r,z;

ω

,t)p(r,z;

ω

,t)>

.sup.1/2

where "r" is the range, "z" is the depth, "ω

" is the frequency of the acoustic signal, "t" is the time, "p*" represents the complex conjugate of the pressure function, and "<

>

" represents an averaging of the function.

26. Apparatus as recited in claim 23 wherein said sampling means includes:

means for obtaining simultaneously complex pressure readings from each of a plurality of predetermined depths at the sampling site by a corresponding pressure transducer means; and

means for determining from the readings the initial acoustic field as a function of depth.

27. Apparatus as recited in claim 26 wherein the readings obtained from each pressure transducer means have the form p(r,z;

ω

,t) and said conversion includes coherently processing the readings to obtain an initial value "P_c " given by

space="preserve" listing-type="equation">p.sub.c =<

p(r,z;

ω

,t)>

where "r" i s the range, "z" is the depth, "ω

" is the frequency of the acoustic signal, "t" is the time, and "<

>

" represents an averaging of the function.

28. Apparatus as recited in claim 26 wherein the readings obtained from each pressure transducer means have the form p(r,z;

ω

,t) and said conversion includes incoherently processing the readings to obtain an initial value "P_r " given by

space="preserve" listing-type="equation">p.sub.I =p.sub.r =<

p*(r,z;

ω

,t)p(r,z;

ω

,t)>

.sup.1/2

where "r" is the range, "z" is the depth, "ω

" is the frequency of the acoustic signal, "t" is the time, "p*" represents the complex conjugate of the pressure function, and "<

>

" represents an averaging of the function.

29. Apparatus as recited in claim 16 wherein said locating means includes:

index processor means generating an index signal having an amplitude corresponding to the amplitude of the backpropagated field at the range and depth; and

index extreme value processor means for determining the extreme value of the index signal based upon a maximum value thereof.

30. Apparatus as recited in claim 29 wherein

said index signal processor means produces, for each iteration of said processing step, an index signal according to